This invention relates to a method of making deep drawn, laminated, non-metallic articles having high ballistic resistance, and more particularly deep drawn, laminated, non-metallic, ballistic-resistant helmets.
In the field of body armor, and more particularly in the production of ballistic-resistant helmets, it has been traditional to rely on metals or metal alloys to provide protection for the head against ballistic missiles and shell fragments or secondary fragments. Metals, however, while providing the required degree of protection, in general have inherent disadvantages, especially weight, and thermal and electrical conductivity. Studies have been conducted with the objective of producing a non-metallic system which will be at least equal to the metallic helmets of the prior art in protective properties and which will be lighter and have other advantages as well. Lightweight ballistic-resistant helmets and helmet liners have been produced from laminates of such non-metallic materials as nylon ballistic cloth, needle-punched nylon felt, woven roving fiber-glass fabric, and polycarbonate sheet. Resin-bonding of a plurality of laminae of such materials has also been employed. More recently, relatively new aromatic polyamides, one of which known as "Kevlar" is manufactured and sold by E. I. duPont de Nemours & Co., have shown greater ballistic resistance than other knonw non-metallic materials and have proven to be approximately equivalent on a weight basis to ballistic steel in ballistic-resistant helmets and also in body armor. These materials in the form of fabrics woven from relatively heavy yarns have been impregnated with resins and molded by compression molding to produce ballistic-resistant helmets. However, use of aromatic polyamides in the making of helmets has proven to be quite expensive, not only because they are relatively new materials, but also because of their inherent tendency to resist shearing, which makes conventional molding operations difficult and expensive, particularly when a cutoff or pinchoff element is employed in forming the edges of helmets, which is the conventional molding practice. The dulling action of "Kevlar" fabric greatly reduces the number of deeply drawn items which can be produced by conventional procedures before renewal of the cutting edges of the mold is required. In addition, even though cutoff may occur, the edges of the deep drawn items are usually fibrillated to a great extent, producing a stubbled edge of such nature that a special edge finishing procedure is required in order to produce a smooth edge on the molded ballistic-resistant item.
It is, accordingly, an object of the invention to provide a method of making a deep drawn, laminated, non-metallic fabric-containing article having high ballistic resistance, the edges of the article being made smooth and substantially free of fibrillation of the fabric or yarn components.
Another object is to provide a method whereby a ballistic-resistant helmet comprising substantial quantities of aromatic polyamide fabric may be produced by molding a resin-impregnated aromatic polyamide fabric without leaving fibrillated aromatic polyamide fibers exposed along the edges of the helmet.
Other objects and advantages will appear from the following description, and the novel features will be particularly pointed out in connection with the appended claims.